Radar systems used to detect the presence, position, and other characteristics of both natural and man-made objects are critical to both civilian and military operations. These systems typically transmit “beams” or electromagnetic (EM) signals toward targets, and process reflected return signals (or echoes) for object identification and characterization. A radar echo return usually contains both signals generated from a target, as well as background clutter. The clutter signal arises from reflections from stationary and slow-moving background objects (rain, land, etc.), and is usually stronger than the target signal. This clutter decreases radar performance by hindering the system's ability to detect targets and/or increases the probability of a false target detection.
Numerous method exist which attempt to discriminate between unwanted clutter and target return signals. Many of these clutter cancellation methods rely on the principle that moving targets have a Doppler frequency shift, while stationary targets do not. Thus, pulse-Doppler radar systems may implement a plurality of Doppler frequency filters (e.g. FFT networks) used to divide the Doppler frequency space into many narrow regions, with each filter corresponding to one of these frequency bands. Knowing the frequency space normally associated with specific clutter types, these Doppler filters can be used to discriminate against clutter, as well as identify target Doppler frequency.
As presently implemented, these systems comprise a plurality of selectable Doppler filter banks, wherein each bank has a series of Doppler filters configured for a specific type of clutter (e.g. weather clutter, ground clutter, “folded over” clutter). A bank selection process may be implemented such that, for example, if a scan area is determined to comprise heavy ground clutter, a single filter bank suited (i.e. matched) for this clutter type will be selected for processing radar returns. In addition to requiring redundant filters found in more than one filter bank (each bank must cover the entire Doppler window), these systems must utilize bank switching controls and associated algorithms which are often difficult to implement and require continuous monitoring of a clutter map to drive the bank switching. Moreover, these bank switching arrangements often do not select the optimum filter bank from a performance perspective.
Accordingly, improved methods of processing return signals in a pulse-Doppler radar system are desired.